LONDON — Barcelona have finally submitted a formal bid for Chelsea defender David Luiz.

The offer will test Jose Mourinho’s resolve to keep the 26-year-old Brazil international, who has long been linked with a move to the Nou Camp, despite Chelsea’s continued insistence that he is not for sale.

If Chelsea do eventually sell Luiz it is likely that they will turn to France international Eliaquim Mangala, but only if Porto drop their asking price of €50 million (S$84.4 million) — the release clause for the 22-year-old central defender who featured for his club in last weekend’s Emirates Cup at Arsenal.

Chelsea would want to pay no more than half that and the latest indications are that Porto might be willing to negotiate.

It is understood that Barcelona made contact with Chelsea yesterday (August 6) regarding Luiz and representatives have arrived in London to submit a bid of just under £34.5 million (S$67.7 million), reports The Daily Telegraph.

Chelsea will reject an offfer of that scale, having indicated to Bayern Munich, who had previously made an inquiry — though not a formal offer — that they would only entertain a deal of €60 million.

Barcelona know that, although Luiz is not agitating to leave Chelsea, he would like to play for them if the opportunity is presented to him.

If Luiz was to leave Stamford Bridge, he has no intention of playing for another Premier League club.

There were suggestions earlier this summer that Luiz might not fit into Mourinho’s plans but this has been strongly refuted by the new manager, and Chelsea.

The player is in the United States on Chelsea’s second pre-season tour, having missed the Far East tour because he played in the Confederations Cup, and has held talks with Mourinho over his future.